Anticorrosion coated steel pipe

ABSTRACT

This invention is to provide a novel anticorrosion coated steel material exhibiting surprising anticorrosion and obtained by providing a coating layer having Pb as a base on the surface of a steel material and fusing an Sn-Cd series alloy against the surface of said coating layer.

United States Patent UNITED STATES PATENTS Domm ..29 /l96.6

Kubo 1 Apr. 25, 1972 s41 ANTICORROSION COATED STEEL 2,386,951 10/1945 Howe ..29/196.6 PIPE 2,323,890 7/1943 Adler..., ..29/l96.6 Inventor: Naomi Kuhn, g y Japan 2,813,805 11/1957 Kendall ..29/ 196.6 [73] Assignee: Usni Kokusal Sangyo Klbnshlkl Keisha, Primary Examiner-Hyland Bizot shlluoka, Japan Armrney- Irving Mi Weiner [22] Filed: Feb. 6, 1970 5 ST C 7 AB RA T [21] Appl. No.: 9,432 l 1 This invention is to provide a novel anticorrosion coated steel I material exhibiting surprising anticorrosion and obtained by '8' ii l providing a coating layer having Pb as a base on the surface of [58] Field fz''ii''f 196.4,194 Steel material and fusing Series alloy against the surface of said coating layer.

[56] References Cited 3 Claims, No Drawings ANTICORROSION COATED STEEL PIPE This invention relates to anticorrosion coated steel materi als.

For an anticorrosion coating of steel pipes have been already practiced Zn, Cu, Pb, Sn and Pb-Sn alloys. Particularly Pb Sn alloys are extensively used as anticorrosion coating materials for steels because they are high in the adhesion and anticorrosion. However, in recent years, a further improvement of the anticorrosion is desired and attempts are being made to improve the coating.

The present invention has been made by discovering that, when a coating layer having Pb as a baseis first provided on the surface of a steel material and an Sn Cd series alloy is then fused as a film onto the surface of said coating layer so that a fused film of said coating layer composition and Sn Cd series alloy composition may be formed on the coating layer having Pb as a base.

Therefore, an object of the present invention is to provide a steel material remarkably high in the anticorrosion by applying a coating layer having Pb as a base and an Sn Cd series alloy without applying a coating of a metal or alloy of a high melting point. H

The coating layer having Pb as a base in the present invention means a coating layer formed of Pb or a lead base alloy. The lead base alloy to be used is preferably of a melting point of 230 to 328C. The Sn Cd series alloy is an alloy containing Sn and Cd with the addition, as required, of a small amount of such metal which reduces the melting point as a melting point adjusting agent as, for example, Zn, Sb or Bi. The rates of Sn and Cd to be used are preferably 63 to 73 parts by weight of Sn and 22 to 32 parts by weight of Cd. Further, when the metal to be added to adjust the melting point is less than parts by weight, a favorable result is obtained.

The fused film can be formed by dipping or passing a steel material coated with a coating layer having Pb as a base in or through a bath of an Sn Cd series alloy at a temperature below and near the melting point of the coating layer. Therefore, this fused film is understood to be a thin layer of a multielement alloy consisting of the composition of the coating tion exhibits an excellent anticorrosion which can never be anticipated from the anticorrosion by only the coating layer having Pb as a base or by only the Sn Cd series alloy not having said coating layer in the lower layer shown in the below mentioned control.

As mentioned above, this fused film is obtained by passing a steel material provided with a coating layer having Pb as a base through a bath of an Sn Cd series alloy maintained at a proper temperature and is uniformly exposed on the surface by the pressure of a wiper provided to remove the bath deposited in excess or is formed between the coating layer having Pb as a base and the Sn Cd series alloy layer.

A coating of Cu or any other metal may not be applied to the surface of a steel material to which the coating layer having Pb as a base is to be applied. In the present invention, unless otherwise specified, merely the steel pipe means a steel material coated or not coated with Cu or any other metal. When a steel material is a steel pipe, the wall surface of the steel material meansboth inside and outside surface or one side surface of the steel pipe.

EXAMPLES l to 4 These examples shall be explained relating to a steel pipe. Preparation of samples:

The samples were prepared by varying the bath temperature of the Sn Cd series alloy for the respective compositions of the coating layer having Pb as a base as mentioned in the below mentioned Table l for the respective examples. Nos. 1 to 4 represent the sample numbers as well as the example numbers. In preparing the sample, in of Nos. 1, 2 and 3, a copper-coated steel pipe of double ply wall structure(a Bundy tube of a copper coating thickness of about 3g) of an outside diameter of 7.94 mm. and a thickness of 0.71 mm. was provided with a coating layer having Pb as a base on the outside surface, was passed through a bath of an Sn Cd series alloy layer and was treated with a wiper. Five pieces of such samples of a length of 1000 mm. were made for each sample number.

Structure steel pipes of an outside diameter of 8 mm. and a thickness of 1.0 mm. not plated with copper were used to prepare the samples of No.4.

Note: (I) Thesignsih fitabfiafethe szime as in the notes in the preceding table.

layer having Pb as a base and the composition of the Sn Cd Tests results? I i series alloy. But, by what action this thin layer exhibits such surprising anticorrosion on the surface of the coating layer having Pb as a base is unknown.

This fused film is obtained, as mentioned above, by maintaining the bath temperature of the Sn Cd series alloy below and near the melting point of the coating layer having Pb as a base and to be an inner layer. When it is applied at a bath temperature lower than this proper temperature range below the melting point, the Sn Cd series alloy forms no multi-element alloy layer with the surface of the coating layer having Pb as a base and therefore no expected anticorrosion is exhibited.

The anticorrosion of this Sn Cd series alloy itself is recognized to be very excellent as-seen in the below mentioned con trols but the anticorrosion obtained by the fon'nation of the coating according to the present invention is understood to be an effect obtained not only by the Sn Cd series alloy but also by forming the above mentioned fused film (multi-element alloy layer) on the surface of the coating layer having Pb as a base, because, as evident by the below mentioned examples, the coating obtained by the invention of the present applica- Testing method:

The tests were made by the following salt water spraying method. That is to say, test pieces made in the above mentioned manner were tightly plugged with a synthetic resin piece at each end, were defatted on the surface and were hung at an angle of inclination of 30 at intervals of 10 mm. in a sealed chamber which was filled with the below mentioned salt water as a spray. The variation with the lapse of time of the rust produced on the surface of each test piece in the atmosphere of this salt water spray was observed and recorded.

. Sannary of the used salt water and apparatus:

1. Purity: Refined sodium chloride of a purity of more than 99.5 percent 3. Th'e'sealed chamber was of a capacity of 0.34m The amount of the sprayed salt water was 3.8 liters/24 hrs.

4. The spraying device consisted of two nozzles. The spraying pressure was 1 kg./cm Test results:

The test results were as shown in Table 2.

However, during the salt water spray test, it was observed that fine white spots were first produced on the coated surface of the steel pipe in the initial period and increased gradually in the number to cover the coated surface, then black spots were produced on the surface covered with the white spots and changed to be red rust spots, the red rust spots changed to be in the form of flows and the coated surface of the steel pipe was gradually covered with the red rust. Therefore, the rusting records in the below mentioned Table 2 show the progress of the rusting by first showing the production of white spots in the initial period of the test, recording only the production of black spots when they were produced, recording only red rust spots when they were recognized and recording only red rust flows when they were recognized.

Tests and results:

The tests were made in the same manner as in the examples. The results were as mentioned in Table 3.

Control 2: Sample No.6:

Five coated steel pipes coated with only an Sn Cd series alloy layer about 3;; thick without applying the coating having Pb as a base in the example mentioned in No.1 in the above mentioned Table l were prepared as samples. The used steel pipes were of the same dimensions and standard as of those used in the examples. Tests and results:

The tests were made in the same manner as in the examples. The results were as mentioned in Table 3.

TABLE 2 672 1,176 1,680 2,018 hours his hours 336 hours hours hours hours hours No. l l W (l 2 Many W siirl';i :i Minty W (otltiro surface). 4 B (4-6) 2 R (2-5) 4 R (3-6) 5 RR (4-8) No. .3 l W (1'2) do ..A(1O e. 3 13(2-4) J R (2 4) 5 11(3-7) 7 RR (6-8) No. .i J W (l 3) 110.. 5 B (2-6) 6 R (1-5) 6 It (4-8) 7 RB (5-9) No. l l W (1-2) .7 .do" 4 B (3-5) 2 B. (1-3) 5 R. (36) 6 RR (44!) Notes: TABLE 3 48 96 168 240 298 336 hours hours hours hours hours hours 1. W: Fine white spots gipgb 8) 5) aggy a l (H a go fi gkfl ase 3- 4-1 a i z a u 2. B: Black spots face). face). face). face). 3. R: Red rust spots No.6 (811- W 4 B R RR 7 RR Cd (en- (3-7) (2-5) (46) (2-7). (6-8). 4. RR: Red rust flows W195)- face).

5. The numerals in the parenthesis represent the maximum value and minimum value of the number of W, B, R or RR produced in the five samples in each example.

about Va that of the case of the above mentioned 7). The others are also like this.

Control 1'.

Sample No.5:

Five coated steel pipes coated in the same manner as in No.l in the above mentioned Table 1 with only the coating Note: I. The signs in the table are the same as in the notes in the preceding table What is claimed is:

1. An anticorrosion coated steel material comprising a steel material, a coating layer having Pb as a base and coating the wall surface of said steel material and an Sn Cd series alloy fused to coat said coating layer, whereby a fused film consisting of said coating layer composition and Sn Cd series alloy composition may be formed on said coating layer having Pb as a base.

2. An anticorrosion coated steel material according to claim 1 wherein on a coating layer having Pb as a base is formed a fused film consisting of said coating composition and an Sn Cd series alloy composition and on said fused film is provided an Sn Cd series alloy layer.

3. An anticorrosion coated steel material according to claim 1 wherein on a coating layer having Pb as a base is formed a fused coating consisting of said coating composition and an Sn Cd series alloy composition and said fused coating is uniformly exposed to the outside surface of the coating layer. 

2. An anticorrosion coated steel material according to claim 1 wherein on a coating layer having Pb as a base is formed a fused film consisting of said coating composition and an Sn - Cd series alloy composition and on said fused film is provided an Sn - Cd series alloy layer.
 3. An anticorrosion coated steel material according to claim 1 wherein on a coating layer having Pb as a base is formed a fused coating consisting of said coating composition and an Sn - Cd series alloy composition and said fused coating is uniformly exposed to the outside surface of the coating layer. 